P2‐purinoceptors of two subtypes in the rabbit mesenteric artery: reactive blue 2 selectively inhibits responses mediated via the P2y‐ but not the P2x‐purinoceptor

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Abstract
α,β‐Methylene ATP and ATP both produced concentration‐dependent contractions of the isolated mesenteric artery of the rabbit that were not inhibited by reactive blue 2. In preparations where the tone had been raised with noradrenaline, ATP and 2‐methylthio ATP, but not α,β‐methylene ATP, produced relaxations of the vessel. These relaxations were inhibited in the presence of reactive blue 2. Reactive blue 2 did not inhibit the contractions to noradrenaline, and only slightly inhibited relaxations to adenosine and acetylcholine. The rank order of potency of purine nucleotide analogues in contracting the vessel was: α,β‐methylene ATP > β,γ‐methylene ATP = 2‐methylthio ATP > ATP, and in relaxing the vessel at raised tone was: 2‐methylthio ATP > ATP > β,γ‐methylene ATP > α,β‐methylene ATP. It is concluded from this study that in the isolated mesenteric artery of the rabbit, purine nucleotides act via P2y‐purinoceptors to cause the muscle to relax and via P2x‐purinoceptors to cause the muscle to contract. The results also suggest that reactive blue 2 selectively inhibits responses mediated via the P2y‐purinoceptor, at least within a limited concentration range.